Stdio.Buffer peculiar state?

I'm trying to hunt down certain long-term-running pgsql issues I'm still
seeing.
While weeding through the backtraces I find the following Stdio.Buffer
state:

Sql.pgsql_util.conxiin(0 bytes, read=[..-1] data=[0..-1] free=[0..8160] allocated)->range_error(1)

What does it take to get a right-hand endpoint of -1 for read and data there?
It seems like the connection is now stuck in a busy loop reading 0 bytes
all the time from the network.
The conxxion class inherits Stdio.Buffer but is only used for read buffering.
-- 
Stephen.